1. Field of the Invention
The present invention relates to an adapter for communicating a first fiber optic connector to a second fiber optic connector. More particularly, the present invention relates to an alignment feature of an adapter, which enables precise alignment of the cores of a multi-core fiber end of the first connector with the corresponding cores of a multi-core fiber end of the second connector.
2. Description of the Related Art
FIG. 1 shows an exploded view of a simplex connector, in the form of an LC connector 30, in accordance with the prior art. The LC connector 30 comprises the following components, from left to right: plug housing 31; ferrule subassembly 32; spring 33; extender 34; and buffer boot 35. For the purposes of the present discussion, the adjectives “front” and “lead” refer to the plug end of a connector (i.e., the left side of FIG. 1). The adjectives “rear” and “tail” refer to the boot end of a connector (i.e., the right side of FIG. 1). Components 31-35 share a common longitudinal axis 36.
In the assembled connector 30, the ferrule subassembly 32 with the cable end mounted thereto, “floats” along longitudinal axis 36 within an enclosure comprising plug housing 31, extender 34, and buffer boot 35. Spring 33 provides spring-loading of the ferrule subassembly 32 within the enclosure, such that the ferrule subassembly 32 is biased toward the front end of plug housing 31. Boot 35 relieves mechanical strain on the optical fiber cable 44.
Ferrule subassembly 32 includes a ferrule 40, a ferrule holder 41 (sometimes referred to as a ferrule barrel), and tubing 42. The ferrule 40 has a precision hole extending down its length, along axis 36. The hole is shaped to closely receive a bare optical fiber from a stripped end of an optical fiber cable 44. The bare fiber is trimmed at the ferrule tip 45 and polished, resulting in an exposed fiber end face 43. Ferrule holder 41 includes a hexagonal flange 46 and a front cone portion 49 having a pair of slots 47, 47′ in its perimeter. The details of the slots 47, 47′ and exposed fiber end face 43 are best seen in the close-up perspective view of the ferrule subassembly 32 shown in FIG. 2.
When connector 30 is fully assembled, the ferrule tip 45 is accessible through an opening 21 at the front of the plug housing 31. The plug housing 31 includes a latch arm 22 that is used to releasably attach the connector 30 into a corresponding socket or jack (not shown).
As best seen in FIG. 3, when connector 30 is fully assembled, the hexagonal flange 46 is seated in a corresponding hexagonal cavity 23 within plug housing 31, thereby limiting rotation of the flange/ferrule assembly 32 around axis 36.
FIG. 4 shows a perspective view of a tuning wrench 50 that can be used to rotate the ferrule subassembly 32 around its longitudinal axis 36 in an assembled connector 30. The ferrule subassembly 32 can be rotated in order to improve core alignment, as will be discussed in relation to FIG. 5. As shown in FIG. 4, the tuning wrench 50 includes a hollow shaft 51 having an opening 52 therein that fits through the plug housing opening 21 and around the ferrule 40. Teeth 53, 53′ engage the pair of slots 47, 47′ in the front cone portion 49 of the ferrule holder 41.
In use, the tuning wrench 50 pushes the ferrule subassembly 32 along its longitudinal axis 36 toward the tail end of the assembled connector 30, such that spring 33 is compressed, and such that hexagonal flange 46 is unseated from its receiving cavity 23 in plug housing 31. Once the hexagonal flange 46 is unseated, the ferrule subassembly 32 can then be freely rotated clockwise or counter-clockwise around its longitudinal axis 36. Releasing the tuning wrench 50 causes the hexagonal flange 46 to be reseated in its receiving cavity 23. It will be appreciated that the ferrule subassembly 32 can only be rotated to one of six orientations (i.e., sixty degree positional tuning) relative to the plug housing 31, corresponding to the six possible engagement locations of the hexagonal flange 46 within the corresponding hexagonal cavity 23 of the plug housing 31.
FIG. 5 illustrates the six potential placements 43A-43F of the exposed fiber end face 43. The reason the exposed fiber end face is not always dead center is due to manufacturing tolerances in getting the fiber core 12 centered in the cladding layer 14, and/or an off-center or canted hole extending down the length of the ferrule 40, and/or the hole in the ferrule 40 is oversized to allow for the epoxy adhering the optical fiber into the hole, and the epoxy is not forming an even layer around the optical fiber within the hole.
Therefore, it is commonly known to view and/or detect the end face 43 of the optical fiber and use the turning wrench 50 to select the one position, shown in bold with reference numeral 43E, out of the six potential positions 43A-43F, which best places the fiber core 12 of the exposed fiber end face 43 in the center of the opening 21 of the plug housing 31. Alternatively the fiber core can be positioned closest to a preferred location, for example 12 o'clock, to maximize transmission between two coupled connectors. The best positioning of the end face 43, e.g., the position which best minimizes the eccentric error, may also be determined with resort to a light measuring detector, which measures the intensity of light being received from the center of the connector end. More details concerning the correction of the eccentric error can be found in US Published Application 2002/0085815, which is herein incorporated by reference.
As can be seen in FIG. 3, the fit between the hexagonal flange 46 and the corresponding hexagonal cavity 23 of the plug housing 31 has significant play 60, 61. A typical hexagon flange 46 has a width dimension of X, e.g., 2.8000 mm, while a typical hexagonal cavity 23 within the plug housing 31 has a width dimension Y, e.g., 3.0700 mm. Based upon these measurements, Applicants have evaluated the play and found that the hexagonal flange 46 may rotated up to +/− twelve degrees within the hexagonal cavity 23 of the plug housing 31. The +/− play is represented by the double headed arrows 60 and 61 in FIG. 3. Such play has been acceptable in the art, wherein the optic fiber 43 presented a single core 12 transmitting light. As one could typically select one of the potential six positions, e.g., a sixty degree optimization, and minimize the eccentric error to a level producing acceptable dB loss across a mated pair of connectors, and the +/− additional twelve degrees of play did not greatly deteriorate the dB loss across the mated pair of connectors.
A current development in the fiber arts is the multi-core optical fiber 43′. As shown in FIG. 6, the multi-core optical fiber 43′ presents multiple cores 12a-12g within a single cladding layer 14. The depiction of FIG. 6 shows a center core 12a and six satellite cores 12b-12g. 
When a first multi-core optical fiber connector 30 mates with a second multi-core optical fiber connector 30A, it is important that each core 12a-12g of the first connector 30 comes into alignment with each core 12a-12g of the second connector 30A. Therefore, the play 60 and 61 depicted in FIG. 3 is not acceptable. A plus or minus twelve degree shift could allow the satellite cores 12b-12g to be completely offset and out of communication when a first multi-core optical fiber connector 30 is mated to a second multi-core optical fiber connector 30A via a pass through adapter.
To address this concern, the prior art of US Published Application 2011/0229085, which is herein incorporated by reference, has reduced the allowable tolerances between the hexagonal flange 46 of the ferrule holder 41 and the hexagonal cavity 23 of the plug housing 31. In US Published Application 2011/0229085, “a tightly toleranced internal hexagonal cavity” is employed, as it is important that the shape geometry employed on the collar of the ferrule holder “match” the shape geometry employed in the internal plug housing. Excessive play, e.g., +/− twelve degrees, would not be acceptable.
In US Published Application 2011/0229085, the external geometry of the ferrule holder, e.g., the hexagonal flange 46, is tightly seated without play into the internal geometry of the plug housing, e.g., the hexagonal cavity 23, relatively rotatable parts of the connector which could affect the angular placement of the satellite cores 12b-12g are preferably locked down in place with epoxy.